Work Function of Cadmium

Abstract

The contact difference of potential Cd-Ba is measured by the electron beam and Kelvin methods. These measurements agree within the limits of reproducibility of either method alone and yield a work function value of 4.08±0.02 ev for the work function of cadmium films deposited on tantalum. The barium surfaces, formed by redistillation following fractional distillation, show their characteristic constancy and reproducibility to ±0.01 ev. Cadmium retains some gas after exhaustive multiple distillation. Measurements taken immediately after deposition of a Cd film and during its aging show (1) that freshly deposited Cd films are generally contaminated with gas which distills with the metal; (2) that the adsorbed gas is removed progressively by getter clean-up with an attendant rise in work function totalling 0.10 ev in extreme cases, and (3) that the work function thus established is constant and reproducible to 0.03 ev or better. Comparison of these measurements with our earlier work on zinc leads to the conclusion that a cadmium surface in equilibrium with the residual gas of a well-gettered tube contains so little adsorbed gas that its final work function can probably be accepted as characteristic of the clean metal.